Android build fails if there is a Java version on the path

[freakboy3742]

If there is a version of Java referenced in the PATH, it is used in preference to the location described by JAVA_HOME. As a result, if that Java version is incompatible with the Android tools (Oracle Java 17 is apparently incompatible with Android), this will cause Android builds to fail.

Reported via #671.

To Reproduce
Steps to reproduce the behavior:

1. Set JAVA_HOME to C:\Program Files\Java (But don't install Java at this location)
2. Install Oracle Java 17, ensuring that C:\Program Files\Common Files\Oracle\Java\javapath ends up in your PATH
3. Generate a hello world project
4. briefcase run android
5. See error

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring project ':app'.
> java.lang.NullPointerException

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 8m 12s

Error while building project.

Expected behavior

Android project should run successfully.

Environment:

• Operating System: Windows (may be reproducible on other operating systems)
• Python version: Any
• Software versions:
  • Briefcase: 0.3.8

Additional context

The original report had an interesting presentation. JAVA_HOME was set, but not set to a valid Java location. Oracle Java 17 was also installed, and this version was in the PATH.

The Java verification is based on trying to invoke %JAVA_HOME%/bin/javac -version; this fails, so Briefcase downloads it's own version of Java and installs it in ~/.briefcase/tools/java.

However, a bare javac does work, executing the Oracle Java version installed at C:\Program Files\Common Files\Oracle\Java\javapath.

Briefcase passes JAVA_HOME into the environment (pointing at the Briefcase version), but doesn't modify the PATH. In this environment, when Gradle invokes javac, it appears that Gradle finds the Oracle version of Java, which breaks the build with the null pointer error.

It's not clear if the JAVA_HOME-ignoring is a Windows behavior, or a Gradle behavior.

There are two pieces required by a the fix:

1. Verify javac -version before verifying %JAVA_HOME%/version
2. Insert JAVA_HOME into the PATH when invoking gradle.

The first ensures that javac (as invoked by gradle) is a valid Java version; the second ensures that the valid version found by briefcase (either Briefcase provided, or user installed) takes priority on the path.

In the meantime, the workaround is to ensure that there isn't a java version in the path.

[rmartin16]

JDK support transitioned from 8 to 17

• Bump JDK 8u242-b08 to 17.0.7+7 #1271